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1.5. Heat driven cooling
desorber, expansion valve and condenser is added to the single
stage cycle (PUMP2, SHEX2, DES2, VB2 and COND2, see diagram
in appendix B.2 page 229).
The desorber (DES1) is now supplied with waste heat from the
upper cycle condenser (COND2). The upper cycle desorber (DES2)
is the only one receiving heat from an external source.
The two cycles are coupled in parallel, which requires further three
components - one splitter and two mixers (SPL, MIXL and MIXR).
Triple stage cycle, parallel flow, COP = 1,7 (200 ◦ C)
This is the same as above, but with yet another cycle on top of the
two. This configuration is also called double condenser coupled.
Quadruple stage cycle, parallel flow, COP = 2,0 (275 ◦ C)
This is the same as above, but with yet another cycle on top of the
three.
Alternatively the water lithium bromide can be configured with series
flow. According to [21] the parallel configuration has a higher COP than
the series configuration at the same operation conditions.
The above mentioned configurations are just a few examples, but
it will be out of the scope of this report to mention all possible
configurations.
The examples show that it is possible to enhance the performance
of an absorption cycle substantially, but it does make the system more
and more complex and expensive. It also appears that cycles with water
lithium bromide has a slightly higher COP than cycles with ammonia
water.
Heat source
Another way to categorize absorptions units is by looking at how the heat
is supplied. Direct fired units use gas-fired combustors whereas indirect
fired units have the heat supplied by hot water or steam. The double (and
triple/quadruple) stage system use either gas-fired combustors or steam
since the input temperature has to be higher than for single stage[29].
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